DESCRIPTION: Environmental stress has been hypothesized as contributing to the development of essential hypertension (EH), particularly in African Americans (AAs) who have a higher prevalence of EH compared to Caucasian Americans (CAs). Exaggerated systemic vascular resistance (SVR) mediated blood pressure (BP) responsivity to stress is one pathway through which environmental stress is thought to be linked to development of EH. Assessment of environmental effects on preclinical markers of EH risk in youth can be observed only with proper control for genetic influences. This can be accomplished using a twin cohort design. Continued examination of the investigator's Twin CV Health cohort (519 pairs of CA and AA twins who will be 14 to 25 years old) for an additional five years will provide the unique opportunity to better understand the effects of Na+ retention as a mechanism augmenting SVR responsivity and changes in vascular function (i.e., endothelium dependent arterial dilation; EDAD), ventricular structure (i.e., left ventricular mass; LVM) and 24-hour ambulatory BP (ABP). The specific aims are to determine: 1) To what extent is environmental stress related to stress induced Na+ retention, SVR responsivity and preclinical markers of EH risk (i.e., decreased EDAD, increased resting BP, ABP, and LVM) and are these relationships stronger in AAs than CAs; 2) Whether stress induced Na+ retention is a pathway linking environmental stress with preclinical markers of EH risk; and 3) Whether behavioral factors (i.e. John Henryism, anger expression, social support, physical activity) moderate effects of environmental stress on stress induced Na+ retention and/or SVR responsivity and in the preclinical markers of EH risk, particularly in AAs. The long-term objectives are to provide a better understanding of environmental stress-related influences on the pathophysiology of EH, which will assist in better identification of youth at increased risk for EH and aid in the development of improved primary prevention programs.